1. Field of the Invention
The present invention relates to an apparatus for establishing a position relative to one or more reference points on an object. More particularly, the invention relates to an apparatus for interaction with a target on a member such as, for example, an automobile body where variations in the target position can be accommodated by the apparatus. After the apparatus has interacted with the target, its position is immobilized so the work can be accomplished on the automobile body in relationship to the target position.
2. Description of the Prior Art
An apparatus for establishing a datum position from an object having dimensional variations is set forth in U.S. Pat. No. 4,813,125, entitled "Method and Apparatus for Establishing the Position of a Datum Reference from an Object Having Dimensional Variations within a Tolerance Range", issued Mar. 21, 1989, to Ernest A. Dacey, Jr. The apparatus of the above referenced patent includes a fixed base structure for rigid mounting to a floor adjacent to an assembly line. A transfer platform is movably attached to the base support structure so that the transfer platform can move in a horizontal direction with respect to the fixed base structure. A support structure assembly is attached to the transfer platform. The assembly can move in a horizontal direction perpendicular to the direction of movement of the transfer platform. A vertical slide assembly is attached to the support structure assembly so that it can move in a vertical direction. Fluid actuated positioning and locating members are attached to the apparatus so that the horizontal and vertical movements can be immobilized subsequent to the attainment of a correct position by utilization of a plurality of probes. The immobilization of each axis of movement of the apparatus is achieved by the action of a pair of opposed fluid driven actuators; thus, to immobilize three axes of movement, six actuators are required.
In U.S. Pat. No. 4,589,199, which issued on May 20, 1987, in the name of Keizaburo Ohtaki et al, an apparatus for assembling an automobile body door is set forth. The patent discloses a set jig that is supported on a shift table positioned adjacent to an automobile assembly line that accommodates automobile components such as the incomplete body structure. The apparatus described in U.S. Pat. No. 4,589,199 is dedicated to the installation of automobile door assemblies to predetermined attachment points that have been established on the automobile body framework. The jig can move from front to rear along the automobile body framework. The movement of the jig is further enhanced by a three-dimensional, right angled coordinate type robot mechanism that is movable with respect to the width and length as well as the height of the automobile body structure. The robot mechanism is provided on a shift table that has a first frame capable of moving along the length of the automobile body. A second movable frame, which is attached to the first frame, is movable in the automobile body width direction. A third movable frame, which is attached to the second frame, is movable in the automobile body height direction.
The robot mechanism can additionally support a door assembly and move it into the proper assembly position on the automobile body. In order to compensate for variations in the location of the door attachment point on the automobile body, a probe is moved into engagement with the door attachment point on the automobile body. If the probe detects any deviation in the location of the door attachment point as compared to where it should be located, the deviation is communicated through electrical means to the robot mechanism so that it can compensate as it moves the door into an attachment position.
Thus, it can be realized that while the above described apparatus permits automobile body deviations to be taken into account during the assembly of a door, the deviation from the normal attachment point must be first ascertained. Then after the probe has been moved into and out of engagement with the automobile body, the actual task of swinging the door panel into an acceptable attachment location can be undertaken. Also, a normal reference point must be established on the assembly line, the automobile body, or both so the probe can successfully calculate the deviation and communicate such deviation to the three axes positioning portion of the apparatus.
A programmable manipulator is described and illustrated in U.S. Pat. No. 4,086,522, which issued on Apr. 25, 1978, in the name of Joseph F. Engelberger et al. The apparatus set forth in this patent is useful in performing welding functions during the assembly of an automobile body frame. The manipulator relies on a complex electrical program with memory retention capacity to store a series of statically taught work positions that are acquired from a stationary workpiece. The computer stored information is then used as a comparison base when the manipulator apparatus is utilized on a moving automobile body assembly line.
Since the manipulator apparatus described in the above mentioned patent forms its motion in accordance with an internally retained memory program, it is difficult to precisely control the location of a tool that is held by the manipulator arm. Variations in automobile bodies is a fact and once the body dimensions move outside the range of the prerecorded deviations, time must be taken to reprogram the memory of the manipulator apparatus so that work on a moving conveyor line can resume. Such recalibration procedure is costly and time consuming in that the conveyor line must be stopped while the memory bank is being reprogrammed.